FIG. 1 is a schematic diagram of a Long Term Evolution (LTE) system including supporting Relay Nodes (RN) according to the related art.
Referring to FIG. 1, a wireless resource management entity includes a macro base station (i.e., an evolved Node B (eNB)) 101 and an RN 102. The RN 102 accesses a core network via another macro base station (i.e., Donor eNB (DeNB)) 103. The DeNB 103 is a base station for RN access, wherein eNBs 101 are connected to each other via an X2 interface, and each eNB 101 is respectively connected to a Mobility Management Entity (MME)/Serving Gateway (S-GW) 104 of the core network via an S1 interface. The RN 102 accesses the DeNB 103 via a Un interface. The DeNB 103 provides an X2 proxy function between the RN 102 and another eNB. The DeNB 103 provides an S1 proxy function between the RN 102 and the MME/S-GW 104. The S1 and X2 proxy functions include transmitting User Equipment (UE) dedicated X2 and S1 signaling between the RN 102 and the eNB 101, the RN 102, and the MME 104, and transmitting between the RN 102 and the S-GW 104.
The existing relay is used for a fixed location and does not support motion between different cells. An example of problem now faced by operators is when a user is on a train moving at a high speed. That is, the service quality provided by the existing relay cannot satisfy the operator's demands on the train at a speed of 250-350 kilometers because of detrimental factors such as high noise, high penetration damage, serious Doppler frequency deviation, and lower handover success rate. To address these problems, research is being performed on a mobile relay. The mobile relay is to address the above problems in the exiting relay, improving the quality of the service that can be provided in the high-speed trains and better satisfying user's demands.
There are two kinds of handover processes in the exiting LTE, i.e. S1 handover and X2 handover.
FIG. 2 describes a handover process of an existing UE, taking S1 handover as an example according to the related art.
Referring to FIG. 2, a source eNB 101a sends a handover required message to an MME 104a in operation 201.
The method by which a UE 100 sends a measurement report to the source eNB 101a and the method by which the source eNB 101a initiates a handover may refer to the existing communications protocol.
In operation 202, the MME 104a sends a handover request message to a target eNB 101b. 
The source base station S-DeNB refers to an eNB where the UE 100 is initially located, and the target base station T-DeNB refers to an eNB where the UE 100 will be switched to.
In operation 203, the target eNB 101b allocates resource for the UE 100 and sends a handover request acknowledgement message to the MME 104a. 
In operation 204, the MME 104a sends a handover command message to the source eNB 101a. 
In operation 205, the source eNB 101a sends a Radio Resource Control (RRC) connection re-configuration message to the UE 100.
In operation 206, the UE 100 is synchronized to the target cell and sends an RRC connection re-configuration completion message to the target eNB 101b. 
In operation 207, the target eNB 101b sends a handover notify message to the MME 104a. 
In operation 208, the MME 104a sends an update bearer request message to a Serving Gateway/Packet Data Network Gateway (S-GW/PDN GW 104b).
The S-GW is mainly used to provide a user plane function and the PDN GW is mainly used to complete functions of billing and lawful interception. The S-GW and the PDN GW may be one entity or two. In this operation, signaling interaction between S-GW and PDN GW is omitted.
In operation 209, the S-GW/PDN GW 104b sends an update bearer response message to the MME 104a. 
In operation 210, the UE 100 initiates a Track Area Update (TAU) procedure.
In operation 211, the MME 104a sends a UE context release command message to the source eNB 101a. 
In operation 212, the source eNB 101a sends a UE context release completion message to the MME 104a. 
It can be seen from the above handover process that each UE needs the interaction of dozens of messages to perform each handover process. The X2 handover process is more optimal than the S1 handover, whereas the RN and the UE both are moving (e.g., on the train) and advancing at a high speed, and if multiple UEs simultaneously perform a handover process, it will lead to an unnecessary waste of resources for the network and will easily lead to a failure of the handover process. In order to address the problem of low handover success rate and improve the efficiency of the handover, the concept of group mobility is set forth. However, there is currently no specific solution about how group mobility is performed.
If an RN and UEs served by the RN simultaneously perform a handover process, a method of ensuring coordinated work is also a problem that cannot be ignored.
In a method provided in the present disclosure, an RN may perform a measurement of a UE and complete a handover process between different cells. Even in this case, there are still two specific problems as described below.
First, when the RN moves from one DeNB to another DeNB (i.e., target DeNB), the MME to which the target DeNB connects may be different from the MME to which the source DeNB connects. So there is a problem of selecting the MME serving the UE, transmitting context information of the UE, and establishing a user plane transmitting path at network side for UE.
Second, there is a problem of letting the UE know of the change of information at the network side, e.g. change of Global Unique Temporary Identifier (GUMMEI) of a new serving MME.
Therefore, it is necessary to provide an effective technical solution to address group movement and group handover.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.